1//===-- llvm/Target/TargetFrameLowering.h ---------------------------*- C++ -*-===//
2//
3//                     The LLVM Compiler Infrastructure
4//
5// This file is distributed under the University of Illinois Open Source
6// License. See LICENSE.TXT for details.
7//
8//===----------------------------------------------------------------------===//
9//
10// Interface to describe the layout of a stack frame on the target machine.
11//
12//===----------------------------------------------------------------------===//
13
14#ifndef LLVM_TARGET_TARGETFRAMELOWERING_H
15#define LLVM_TARGET_TARGETFRAMELOWERING_H
16
17#include "llvm/CodeGen/MachineBasicBlock.h"
18#include <utility>
19#include <vector>
20
21namespace llvm {
22  class CalleeSavedInfo;
23  class MachineFunction;
24  class RegScavenger;
25
26/// Information about stack frame layout on the target.  It holds the direction
27/// of stack growth, the known stack alignment on entry to each function, and
28/// the offset to the locals area.
29///
30/// The offset to the local area is the offset from the stack pointer on
31/// function entry to the first location where function data (local variables,
32/// spill locations) can be stored.
33class TargetFrameLowering {
34public:
35  enum StackDirection {
36    StackGrowsUp,        // Adding to the stack increases the stack address
37    StackGrowsDown       // Adding to the stack decreases the stack address
38  };
39
40  // Maps a callee saved register to a stack slot with a fixed offset.
41  struct SpillSlot {
42    unsigned Reg;
43    int Offset; // Offset relative to stack pointer on function entry.
44  };
45private:
46  StackDirection StackDir;
47  unsigned StackAlignment;
48  unsigned TransientStackAlignment;
49  int LocalAreaOffset;
50  bool StackRealignable;
51public:
52  TargetFrameLowering(StackDirection D, unsigned StackAl, int LAO,
53                      unsigned TransAl = 1, bool StackReal = true)
54    : StackDir(D), StackAlignment(StackAl), TransientStackAlignment(TransAl),
55      LocalAreaOffset(LAO), StackRealignable(StackReal) {}
56
57  virtual ~TargetFrameLowering();
58
59  // These methods return information that describes the abstract stack layout
60  // of the target machine.
61
62  /// getStackGrowthDirection - Return the direction the stack grows
63  ///
64  StackDirection getStackGrowthDirection() const { return StackDir; }
65
66  /// getStackAlignment - This method returns the number of bytes to which the
67  /// stack pointer must be aligned on entry to a function.  Typically, this
68  /// is the largest alignment for any data object in the target.
69  ///
70  unsigned getStackAlignment() const { return StackAlignment; }
71
72  /// getTransientStackAlignment - This method returns the number of bytes to
73  /// which the stack pointer must be aligned at all times, even between
74  /// calls.
75  ///
76  unsigned getTransientStackAlignment() const {
77    return TransientStackAlignment;
78  }
79
80  /// isStackRealignable - This method returns whether the stack can be
81  /// realigned.
82  bool isStackRealignable() const {
83    return StackRealignable;
84  }
85
86  /// getOffsetOfLocalArea - This method returns the offset of the local area
87  /// from the stack pointer on entrance to a function.
88  ///
89  int getOffsetOfLocalArea() const { return LocalAreaOffset; }
90
91  /// isFPCloseToIncomingSP - Return true if the frame pointer is close to
92  /// the incoming stack pointer, false if it is close to the post-prologue
93  /// stack pointer.
94  virtual bool isFPCloseToIncomingSP() const { return true; }
95
96  /// assignCalleeSavedSpillSlots - Allows target to override spill slot
97  /// assignment logic.  If implemented, assignCalleeSavedSpillSlots() should
98  /// assign frame slots to all CSI entries and return true.  If this method
99  /// returns false, spill slots will be assigned using generic implementation.
100  /// assignCalleeSavedSpillSlots() may add, delete or rearrange elements of
101  /// CSI.
102  virtual bool
103  assignCalleeSavedSpillSlots(MachineFunction &MF,
104                              const TargetRegisterInfo *TRI,
105                              std::vector<CalleeSavedInfo> &CSI) const {
106    return false;
107  }
108
109  /// getCalleeSavedSpillSlots - This method returns a pointer to an array of
110  /// pairs, that contains an entry for each callee saved register that must be
111  /// spilled to a particular stack location if it is spilled.
112  ///
113  /// Each entry in this array contains a <register,offset> pair, indicating the
114  /// fixed offset from the incoming stack pointer that each register should be
115  /// spilled at. If a register is not listed here, the code generator is
116  /// allowed to spill it anywhere it chooses.
117  ///
118  virtual const SpillSlot *
119  getCalleeSavedSpillSlots(unsigned &NumEntries) const {
120    NumEntries = 0;
121    return nullptr;
122  }
123
124  /// targetHandlesStackFrameRounding - Returns true if the target is
125  /// responsible for rounding up the stack frame (probably at emitPrologue
126  /// time).
127  virtual bool targetHandlesStackFrameRounding() const {
128    return false;
129  }
130
131  /// emitProlog/emitEpilog - These methods insert prolog and epilog code into
132  /// the function.
133  virtual void emitPrologue(MachineFunction &MF) const = 0;
134  virtual void emitEpilogue(MachineFunction &MF,
135                            MachineBasicBlock &MBB) const = 0;
136
137  /// Adjust the prologue to have the function use segmented stacks. This works
138  /// by adding a check even before the "normal" function prologue.
139  virtual void adjustForSegmentedStacks(MachineFunction &MF) const { }
140
141  /// Adjust the prologue to add Erlang Run-Time System (ERTS) specific code in
142  /// the assembly prologue to explicitly handle the stack.
143  virtual void adjustForHiPEPrologue(MachineFunction &MF) const { }
144
145  /// Adjust the prologue to add an allocation at a fixed offset from the frame
146  /// pointer.
147  virtual void adjustForFrameAllocatePrologue(MachineFunction &MF) const { }
148
149  /// spillCalleeSavedRegisters - Issues instruction(s) to spill all callee
150  /// saved registers and returns true if it isn't possible / profitable to do
151  /// so by issuing a series of store instructions via
152  /// storeRegToStackSlot(). Returns false otherwise.
153  virtual bool spillCalleeSavedRegisters(MachineBasicBlock &MBB,
154                                         MachineBasicBlock::iterator MI,
155                                        const std::vector<CalleeSavedInfo> &CSI,
156                                         const TargetRegisterInfo *TRI) const {
157    return false;
158  }
159
160  /// restoreCalleeSavedRegisters - Issues instruction(s) to restore all callee
161  /// saved registers and returns true if it isn't possible / profitable to do
162  /// so by issuing a series of load instructions via loadRegToStackSlot().
163  /// Returns false otherwise.
164  virtual bool restoreCalleeSavedRegisters(MachineBasicBlock &MBB,
165                                           MachineBasicBlock::iterator MI,
166                                        const std::vector<CalleeSavedInfo> &CSI,
167                                        const TargetRegisterInfo *TRI) const {
168    return false;
169  }
170
171  /// hasFP - Return true if the specified function should have a dedicated
172  /// frame pointer register. For most targets this is true only if the function
173  /// has variable sized allocas or if frame pointer elimination is disabled.
174  virtual bool hasFP(const MachineFunction &MF) const = 0;
175
176  /// hasReservedCallFrame - Under normal circumstances, when a frame pointer is
177  /// not required, we reserve argument space for call sites in the function
178  /// immediately on entry to the current function. This eliminates the need for
179  /// add/sub sp brackets around call sites. Returns true if the call frame is
180  /// included as part of the stack frame.
181  virtual bool hasReservedCallFrame(const MachineFunction &MF) const {
182    return !hasFP(MF);
183  }
184
185  /// canSimplifyCallFramePseudos - When possible, it's best to simplify the
186  /// call frame pseudo ops before doing frame index elimination. This is
187  /// possible only when frame index references between the pseudos won't
188  /// need adjusting for the call frame adjustments. Normally, that's true
189  /// if the function has a reserved call frame or a frame pointer. Some
190  /// targets (Thumb2, for example) may have more complicated criteria,
191  /// however, and can override this behavior.
192  virtual bool canSimplifyCallFramePseudos(const MachineFunction &MF) const {
193    return hasReservedCallFrame(MF) || hasFP(MF);
194  }
195
196  // needsFrameIndexResolution - Do we need to perform FI resolution for
197  // this function. Normally, this is required only when the function
198  // has any stack objects. However, targets may want to override this.
199  virtual bool needsFrameIndexResolution(const MachineFunction &MF) const;
200
201  /// getFrameIndexOffset - Returns the displacement from the frame register to
202  /// the stack frame of the specified index.
203  virtual int getFrameIndexOffset(const MachineFunction &MF, int FI) const;
204
205  /// getFrameIndexReference - This method should return the base register
206  /// and offset used to reference a frame index location. The offset is
207  /// returned directly, and the base register is returned via FrameReg.
208  virtual int getFrameIndexReference(const MachineFunction &MF, int FI,
209                                     unsigned &FrameReg) const;
210
211  /// Same as above, except that the 'base register' will always be RSP, not
212  /// RBP on x86.  This is used exclusively for lowering STATEPOINT nodes.
213  /// TODO: This should really be a parameterizable choice.
214  virtual int getFrameIndexReferenceFromSP(const MachineFunction &MF, int FI,
215                                          unsigned &FrameReg) const {
216    // default to calling normal version, we override this on x86 only
217    llvm_unreachable("unimplemented for non-x86");
218    return 0;
219  }
220
221  /// processFunctionBeforeCalleeSavedScan - This method is called immediately
222  /// before PrologEpilogInserter scans the physical registers used to determine
223  /// what callee saved registers should be spilled. This method is optional.
224  virtual void processFunctionBeforeCalleeSavedScan(MachineFunction &MF,
225                                             RegScavenger *RS = nullptr) const {
226
227  }
228
229  /// processFunctionBeforeFrameFinalized - This method is called immediately
230  /// before the specified function's frame layout (MF.getFrameInfo()) is
231  /// finalized.  Once the frame is finalized, MO_FrameIndex operands are
232  /// replaced with direct constants.  This method is optional.
233  ///
234  virtual void processFunctionBeforeFrameFinalized(MachineFunction &MF,
235                                             RegScavenger *RS = nullptr) const {
236  }
237
238  /// eliminateCallFramePseudoInstr - This method is called during prolog/epilog
239  /// code insertion to eliminate call frame setup and destroy pseudo
240  /// instructions (but only if the Target is using them).  It is responsible
241  /// for eliminating these instructions, replacing them with concrete
242  /// instructions.  This method need only be implemented if using call frame
243  /// setup/destroy pseudo instructions.
244  ///
245  virtual void
246  eliminateCallFramePseudoInstr(MachineFunction &MF,
247                                MachineBasicBlock &MBB,
248                                MachineBasicBlock::iterator MI) const {
249    llvm_unreachable("Call Frame Pseudo Instructions do not exist on this "
250                     "target!");
251  }
252};
253
254} // End llvm namespace
255
256#endif
257